Wednesday, December 05, 2007

Northern Saw-whet Owls '07

Kelly holding one of the three owls we caught.
Look at those tiny, needle-sharp talons.

I finally got a chance to go owl banding this year. Kelly Jones and I went down to Yellowwood state forest on 11/24 to help the team of biologists in their research on Northern Saw-whet Owls. This was a big migration year for this species, with a record number of migrating owls captured and banded. I love to see these gorgeous birds up close.

Here are the season's stats from the lead bander, Ross Brittain. I thought this was very interesting.

YSF Totals:
Hatch Year = 134 (68.4%)
After Hatch Year = 10 (5.1%)
Second Year = 32 (16.3%)
After Second Year = 20 (10.2%)
Female = 136 (69.4%)
Male = 17 (8.7%)
Unknown = 43 (21.9%)

YSF Main = 124 NSWOs
YSF Sub = 72 NSWOs
Grand Total = 196 NSWOs

Foreign Recaps = 4 (2 from Linwood Springs, WI, 1 from Ontario and 1?)
Local Recaps = 10 local recap NSWOs, average 4.9 days between captures and 2.1 grams of weight lost.

A few notes on demographics... our previous five-year average is ~53% HY owls, but when I throw out two unrepresentative years (2004 & 2005) the other three years averaged 62% HY owls. The previous five years have ranged from 78-85% Females and generally 5-6% Males. Thus, we had fewer confirmed females in the population this year, and more males, compared to the previous five years. The lower female population is likely due to the fact that they weighed less from lower fat reserves
and were actually classified as unknowns. I will be able to analyze this later.

Both the Main and Sub station caught ~68% HYs, ~5% AHYs, ~16% SYs, and ~10% ASYs. However, the Main station had 75% Females compared to only 59.7% at the sub station. The Main station had 8% Males, and sub had 9.7% Males. The big difference was in the Unknown owls, the Main station had 17% Unknowns and the sub station had 30.6% Unknowns.

I will give you a more complete description of the southern Indiana season once I receive the data from Jess Gwinn's station in Newark.

Adding our 196 to Jess's 248 brings us to a total of 444 NSWOs this season. What a nice round number that happens to be 10 more than our previous 5 years combined.

One amazing thing is that we only had 10 local recapture NSWOs this year in YSF. We had 13 in YSF in 2003 when we only captured a total of 70, and they averaged 11 days between captures. This is good evidence that the NSWOs were not hanging around YSF this year.

Thanks for all of the great help this year! Happy Holidays!
Ross Brittain
Indiana NSWO Banding Coordinator

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